In a rotary actuator disk drive system, data is recorded on and/or reproduced from a plurality of substantially circular, concentric data tracks or disks. A head actuator is provided upon which a plurality of read/write heads are mounted, and the head actuator is pivotally mounted in an actuator housing by means of a shaft assembly for moving the heads along bi-directional, arcuate paths over their respective disks to position the heads at selected tracks.
Unfortunately, it is possible for an electrical failure, in the servo controller or related circuitry, to cause the actuator to move at full speed in either direction of travel. If this occurs, and some mechanism is not provided to stop the actuator during such a failure, the actuator will "crash" into the mechanical limit of its travel. Such a crash may not only seriously damage the actuator mechanism, but may also result in excessive deceleration, causing the read/write heads, which are positioned very close to the disk surface, to strike the disk surface, thereby causing damage to both the heads and the disk surface.
In the event of such an electrical failure, an emergency mechanical apparatus is necessary to stop the travel of the accessing mechanism in a controlled manner to avoid damage to the actuator, the heads or the disk file. That is, the deceleration of the actuator should not exceed a certain maximum.
In prior art systems, two stop mechanisms were generally spaced at each limit position of the actuator or alternately at limit positions of some other component of the accessing mechanism. Generally, the crash stops were not preloaded and thus there was no initial stopping force. A preloaded crash stop is also known to provide an immediate stopping force on contact with the actuator. Ideally, the crash stop is a solid piece of material (e.g. steel); but this produces a large rebound shock, that is, a large deceleration, on the pivoting actuator carriage on initial contact which could damage the head suspension mounted on the carriage.
Therefore, most prior art implementations have been in the form of elastomeric bumpers. These have the disadvantage of requiring a significant amount of disk space because (1) the crash stop is not preloaded, hence a larger deflection is required for a given limit on actuator deceleration, and (2) space must be provided to accommodate variations in crash stop location due to tolerance variations in the parts from which the disk drive system is assembled.